CoMP (Coordinated Multi-Point) system may be used to improve the throughput of at cell-boundary users using the improved MIMO (Multiple Input Multiple Output) transmission in multi-cell environment. In case of applying the CoMP system, inter-cell interference may be reduced in multi-cell environment. A UE may also simultaneously receive a data from multi-cell base-station performing CoMP operation.
In addition to, each eNB may improve the performance of the system by supporting one or more UEs using the same radio frequency. Furthermore, an eNB may perform SDMA (Space Division Multiple Access) method based on channel state information between UE and eNB.
CoMP operation scheme includes joint processing (JP) scheme of cooperative MIMO through data sharing and coordinated scheduling scheme/beamforming (CS/CB) scheme.
Serving cell and one or more collaborative cells may be connected to scheduler through the backhaul or x2 interface. Scheduler may receive channel state information which is measured by each eNB through the backhaul. For example, cooperative MIMO operation is scheduled by scheduler for serving eNB and one or more cooperative eNBs. That is, scheduler can directly command for cooperative MIMO operation to each eNB.
As described above, a UE may receive signals from multiple transmission points such as multi-cell operation (e.g. dual cell operation or CoMP Tx/Rx). In this case, there are several consideration points. First of all, multiple cells are required to align timing (Tx timing) alignment so that the corresponding UE receiving signals from multiple cells can easily process and achieve throughput/diversity gain.
Assuming the timing mismatch is less than CP length of received signal, the joint processing scheme in the receiver (e.g., UE, eNB or Relay Node) may be coherent combining or non-coherent combining depending on the used multi-point transmission model(s).
Consider that coherent combining is expected as one of multi-point transmission scheme. Then a signal transmitted from the multi-point need to be coherently combined at the receiver antenna, which can be ensured by phase correction at each transmission point which is obtained by the UE feedback before CoMP transmission.
However, this combined signal may not result in a fully coherent signal even in case of the same number/position of resource elements (REs) transmission and the same MCS (Modulation and Coding Scheme)/MIMO modes. This situation may happen when the ratio between data RE and reference symbol RE do not have the same ratio between the transmission points.
However, a method for the coherent reception at one receiver has not studied yet.